How to Identify and Resolve Water Hammer:

A Plumber’s Guide

Our best visual representation of Water Hammer💧🔨🤣

Have you ever heard loud banging, thudding, or whistling noises coming from your pipes? This unsettling sound, known as water hammer, results from a pressure shock wave within your plumbing system. Water hammer can be not only very noisy but also lead to burst pipes, damaged valves, and other plumbing issues. In this guide, we’ll explore what water hammer is, its common causes, and the steps you can take to fix it.

What Is Water Hammer?

Figure 2: This is a video showing water hammer in action from a vanity basin. (Sound On 🔊)

Water hammer occurs when a moving column of water suddenly stops or changes direction, creating a shock wave that travels through your pipes. When this shock wave hits a valve or dead end, it results in a loud banging noise—hence “water hammer.”

Most commonly, this happens when a fixture like a washing machine or tap valve is turned on or off quickly. The rapid change in water flow generates pressure surges that cause noticeable noise and vibrations in your plumbing. These surges can manifest as whistling, screeching, shuddering, or vibrating pipes.

Besides being noisy, water hammer can put significant stress on your plumbing system. Repeated shock waves can weaken pipe joints, valves, and fixtures over time, potentially leading to leaks or other damage if not addressed. Recognising water hammer and its signs can help you take preventative measures to protect your plumbing.

Common Causes of Water Hammer

Identifying the root cause of water hammer can be challenging because the banging noise often originates from a different location than the fixture or appliance in use. For instance, turning off a kitchen tap can cause water hammer in the bathroom.  Adding to the challenge, the issue is often intermittent may not be able to be reliability reproduced.

As maintenance plumbing experts, here are some of the most common culprits we see:

1. Hot Water System Valves

Old hot water system valves, such as duo valves and pressure limiting valves, can cause water hammer. Below is an example of a water hammer issue we resolved for a customer in Toowong, Brisbane by replacing the old T-head valve at the hot water system with a duo valve.

Image: Problem solved – identifying and replacing a hot water valve contributing to water hammer.

2. Fast Closing Valves (i.e. solenoids)

Appliances like dishwashers and washing machines use solenoid valves that shut off water flow abruptly. Old mixer taps with stiff handles are also common culprits, as the cartridge becomes stiff and shuts off suddenly.

Image: An old mixer tap with a stiff handle that caused a loud water hammer.

3. High Water Pressure

Excessive water pressure can significantly exacerbate the effects of water hammer, increasing noise and stress on your plumbing system. According to the Australian plumbing standards:

AS/NZS 3500.1-2003, Clause 3.3.4 – Maximum Pressure Within Buildings

“The maximum static pressure at any outlet, other than a fire service outlet, within a building shall not exceed 500 kPa.”

Pressures above 500 kPa can cause damage from water hammer, reduce the lifespan of appliances, taps, and fittings, and lead to excessive noise in the system.

Many suburbs in Brisbane, such as St Lucia, have water pressure far exceeding 500 kPa. Properties in these areas are highly susceptible to water hammer. If you live in an area with high water pressure, consider installing pressure limiting valves to protect your plumbing system. You can find out more about pressure limiting valves here.

4. Damaged Tapware or Washers

Damaged or worn washers in taps and valves can contribute to water hammer. Below is a set of ceramic disc taps in a shower that had failed internally and was causing water hammer in a unit complex. This was resolved by replacing the tapware. Note this is most common in localised area.

Image: Failed ceramic disc taps causing water hammer.

5. Loose Pipes

Unsecured pipes can move and bang against walls or studs when water flow stops suddenly. This is especially common in Queenslander or raised-style houses, where pipework under the house may be suspended and require extra clips. Depending on whether the pipework is copper, poly, or plastic, different spacing and securing methods are necessary. Loose pipes can be very challenging to resolve if there is no access, for example if pipework is run inside wall cavities.

6. Blocked Aerators or Debris in the Line

Dirt or Debris in the line can contribute to water hammer. An example we occasionally see is kitchen mixer aerator which can block up with debris. This creates backpressure and results in water hammer.

Identifying Water Hammer in Your Home

A clear understanding of what is causing the phenomenon in your home is key to identifying the right solution. For the best chance of a positive result, before engaging a plumber, it can be beneficial to keep a log of what taps, toilets, dishwashers, washing machines, or irrigation/plumbing fixtures are causing the water hammer to manifest and at what time of day the issue is arising.

Steps to Identify Water Hammer:

1. Listen Carefully: Note when and where the banging noises occur.
2. Check Appliances: Observe if the noise happens when certain appliances are running.
3. Inspect Fixtures: Look for any visible movement in pipes when the noise occurs. Record if it is just one point or is both hot and cold.
4. Monitor Water Usage: Keep a log of which taps or fixtures are in use when you hear the noise.

How to Stop Water Hammer

Unfortunately, there’s no one-size-fits-all solution. Addressing the issue often requires a process of elimination, starting with the most likely causes. This can be time-consuming and may involve multiple visits. Due to the nature of the problem, a successful outcome isn’t always guaranteed, and ongoing monitoring may be necessary.

Possible Solutions:

1. Repair or Replace Faulty Fixtures

Worn-out washers and old valves may need to be repaired or replaced to ensure they aren’t contributing to the problem. Most commonly, hot water valves such as the duo (isolation, non-return valve) and PLV (pressure limiting valve). This requires a systematic approach of replacing the ‘most-likely’ next culprit.  Unfortunately, there is often no real way to test if this will be successful before carrying out the work.

2. Limit Water Pressure

High water pressure can intensify water hammer. Installing a pressure-reducing valve can help maintain optimal water pressure levels. If your property has pressure over 500 kPa, this may also increase the longevity of taps, fittings, and flexi hoses. For more information on the damage high water pressure can cause, read our blog on protecting your home from a burst flexi hose.

3. Secure Loose Pipes

Use pipe clips to secure loose pipes, preventing them from moving and banging against surfaces. Unfortunately, this is not always possible or practical, especially when there is no access to the pipes.

4. Install Water Hammer Arrestors

Water hammer arrestors are devices designed to absorb the shock waves created when water flow stops abruptly, thereby reducing or eliminating the banging noises in your pipes. They are typically installed near the source of the water hammer, such as dishwashers, washing machines, or fixtures with quick-closing valves.

While water hammer arrestors can be effective in mitigating the immediate symptoms of water hammer, they are often considered a temporary or supplementary solution. In our experience, the success of using arrestors has been mixed. It’s important to note that these devices have a finite lifespan; the internal components can wear out over time, requiring replacement to maintain their effectiveness.

Ideally these devices should be installed and orientated at the end of a line to absorb the shock.

Image: A water hammer arrestor installed near a washing machine. This was installed as a last resort and provided some temporary relief by reducing the severity of the water hammer.